The light-emitting diodes of III-V group nitrides were known since 1995. The manufacturing yield and properties have been improved continuously in the recent years. Light-emitting diodes were developed, which lack the blue color of the three primary colors in the visible light spectrum and further the light-emitting diodes were developed which generate white light by mixing colors of generated light wherein the light-emitting diode with the blue light is an important element for the light-emitting diode with white light. Generation of imitated white light produced by mixing blue light with yellow light or the white light produced by mixing red and green light with yellow light is the important application for the light-emitting diodes of III-V group nitrides.
Please refer to the FIG. 1A and FIG. 1B. The common light-emitting diode chip comprises a sapphire substrate 11′, a N type BGaN layer 12′, an InGaN multiple quantum wells layer 13′, P type GaN layer 14′, N type electrode 15′, P type electrode 16′ and a seal and package layer 17′. When the light emits from the InGaN multiple quantum wells layer 13′, the light has no specific transmission direction. The light propagates in all directions so only a part of the light will emit from the top of the light-emitting diode chip. Accordingly, common light-emitting diode chips have low taking out efficiency of the light and only up to 50% of the generated light emits from the surface of the light-emitting diode chip. A portion of 50% light will be absorbed by P type electrode 16′, to further reduce the light take out. White light is composed of the blue, green and red lights generated in radiating layers of the chip or is produced by adding the fluorescence powder into the radiating layers. At present, only a single seal and package layer is used to seal the light-emitting diode with the white light. Because the blue, green and red light have different transmissions for seal and package layers due to the different refractive indexes thereof, use of a single seal and package layer may reduce the light strength of the mixed blue, green and red lights in the conventional LEDs.
A light-emitting diode structure of III-V group nitrides with light reflection layer of multiple films and the manufacturing method is presented in Taiwan Patent No. 229954 which was filed on 29 Jun. 2004. The patent discloses the light-emitting diode structure of III-V group nitrides with light reflection layer of multiple films, which has a light reflection layer of multiple films deposited each on the other up above the covering layer of N type GaN and below the transparent electric conduction film and formed from two materials having different refractive coefficients. The light reflection layer of multiple films connects with a part of P type electrode, N type electrode and in contact with a layer of N type Ω. The light reflection layer of multiple films is used for covered crystal structure and reflective light.
Accordingly, when red, green and blue lights are mixed to form light-emitting diode with white light, these three wavelengths have different transmissions for the seal and package layer. When the light-emitting diode emits lights of different wavelengths, increase of the taking out efficiency of the light is a very important issue.